Conformation-induced volatile and nonvolatile conductance switching effects were demonstrated in non-conjugated polymers containing the same electroactive pendant groups. Single-layer devices of the structure indium-tin-oxide/polymer/aluminum were fabricated from two non-conjugated polymers with pendant carbazole groups in different spacer units. The device based on poly(2-(N-carbazolyl)ethyl methacrylate) (PMCz) exhibited nonvolatile write-once-read-many-times (WORM) memory behavior with an ON/OFF current ratio up to 106, while the device based on poly(9-(2-((4-vinylbenzyl)oxy)ethyl)-9H-carbazole) (PVBCz) exhibited volatile memory behavior with an ON/OFF current ratio of approximately 103. The formation of carbazole excimers resulting from conformation-induced conductance switching under an electric field was revealed in situ by fluorescence spectroscopy. The corresponding voltage-induced conformation ordering in the polymer film was captured by transmission electron microscopy. In the absence of a spacer unit between the pendant carbazole group and the main chain, regioregular poly(N-vinylcarbazole) (PVK) exhibited only one conductivity state (ON state). The differences in memory behavior among the three polymers were attributed to their inherent differences in the degree of regioregularity and ease of conformational relaxation of the field-induced regioregular carbazole groups. These conformational effects were in turn dictated by the chemical structure and steric effect of the spacer unit between the pendant carbazole group and the main chain.

Electronic memory devices having the indium-tin oxide/polymer/Al sandwich structure were fabricated from polymers containing pendant azobenzene chromophores in donor-acceptor structures. The reversibility, or rewritability, of the high-conductivity (ON) state was found to be dependent on the terminal moiety of the azobenzene chromophore. While the polymers with electron-accepting terminal moieties (-Br or -NO2) in the pendant azobenzene exhibit write-once, read-many-times (WORM) type memory behavior, those with electron-donating terminal moieties (-OCH3) exhibit rewritable (FLASH) memory behavior. The WORM memory devices have low switching ("write") voltages below -2 V and high ON/OFF current ratios of about 10(4)-10(6). The polarity of the "write" voltage can be reversed by using an electrode with a higher work function than Al, thus excluding metallic filamentary conduction as a cause of the bistable switching phenomenon. The FLASH memory devices have low "write" and "erase" voltages of about -1.7 to -1.8 V and 2.0 to 2.2 V, respectively, and ON/OFF current ratios of about 10(3)-10(4). The electrical bistability observed can be attributed to charge trapping at the azobenzene chromophores, resulting in the charge-separated, high-conductivity state. The proposed mechanism is supported experimentally by a red shift and peak broadening in the UV-visible absorption spectra of the polymer films resulting from the OFF-to-ON electrical transition.

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P-doping of conjugated polymers requires electron transfer from the conjugated polymer to the p-dopant. This implies that the highest occupied molecular orbital (HOMO) of the conjugated polymer has to be higher than the lowest unoccupied molecular orbital (LUMO) of the p-dopant. Although commonly used p-dopants such as 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) have a low LUMO of −5.24 eV, most conjugated polymers used in high-performance field-effect transistors are donor–acceptor-type polymers with deep HOMO values, making them difficult to be effectively doped by F4TCNQ. Here, we utilized the proquinoidal 2,6-dialkyl-benzo­[1,2-d;4,5-d′]­bistriazole (BBTa26) moiety in conjugated polymers to destabilize HOMO, allowing effective p-doping using very dilute F4TCNQ solutions. The extent of the quinoidal character and hence their intrinsic conductivities and the ability to be doped are dependent on the dihedral angles and aromaticity of the aryl spacer groups along the polymer backbone. Intrinsic conductivities as high as 10–2 S cm–1 were achieved. Upon doping using F4TCNQ, highly delocalized polarons were observed. As such, electrical conductivities of over 100 S cm–1 and an enhancement of the Seebeck coefficient from carrier-induced softening can be achieved. A maximum power factor of 11.8 μW m–1 K–2 was achieved in thin-film thermoelectric devices. These results are among the highest for solution-phase p-doping using F4TCNQ without additional processing.